Profits from animal trafficking are between $8 billion to $10 billion a year, most of which are used to fund narcotics and human trafficking, according to Kerry.

Commercial ivory trade was banned in the United States in 1989. The crushing of the six-ton stockpile of elephant ivory near Denver is the first time the U.S. has destroyed such large quantities.

The ivory was seized and maintained as evidence until court trials were completed. Once the cases were concluded, some of it was used for training law enforcement officers.

"Over the past 25 years, we have accumulated far more elephant ivory than we can use for these purposes, and decided to destroy this material as a demonstration of our commitment to combating wildlife trafficking," the U.S. Fish and Wildlife Service said.

The illegal ivory trade has doubled worldwide since 2007, with the United States the second-largest retail market for illegally acquired ivory. China is the largest market.

Poaching of the rhino horn is also a lucrative industry. Much of the loot is sold to the affluent in Asia, where some believe the horns cure a series of ills, including cancer and hangovers, and can boost virility.

Last year alone, about 745 rhinos were poached throughout Africa -- the highest number in two decades. Some rhinoceros subspecies have been declared extinct.

Conservation groups say the recent surge in the illicit ivory trade has resulted in the killing of 30,000 African elephants annually in recent years.

Other nations including the Philippines, Kenya and Gabon have destroyed large quantities of ivory in recent years.